This invention relates to a method of depositing silicon oxide films on the surface of semiconductor substrates, and more particularly to depositing such films by chemical vapor deposition using alkylsiloxane oligomers precursors with ozone.
Chemical vapor deposition (CVD) of silicon dioxide is a widely used manufacturing technology for the deposition of dielectric films or layers used in the production of semiconductors. There are two main CVD processes currently used to deposit silicon dioxide (SiO2) on semiconductor substrates or wafers. The two main processes are a silane/oxygen (SiH4/O2) process and a triethoxysilane/ozone (TEOS/O3) process. Of these, the TEOS/O3 process has been widely employed in semiconductor manufacturing due to the superior quality of the SiO2 films deposited by this process, especially with regard to the gap filling capability of the film. This advantage becomes especially important in light of the decreasing feature sizes and increasing aspect ratios of the semiconductor device features in the present day very large scale integrated (VLSI) manufacturing. Thus, efforts have been made to enhance the gap filling capability of the TEOS/O3 process.
Apart from the work on understanding and improving the TEOS/O3 process for better gap fill ability, efforts have also been made to identify new organosilicon precursors that could be used to deposit SiO2 films of quality superior or comparable to those deposited by the TEOS/O3 process. These new organosilicon precursors include hexamethyldisiloxane (HMDSO), hexamethyl disilazane (HMDS), octamethylcyclotetrasiloxane (OMCTS) and 2,4,6,8-tetramethylcyclo tetra siloxane (TMCTS). The SiO2 films deposited from these precursors had properties similar or poorer compared to the films deposited using TEOS/O3 and therefore offered no advantage over the already very established TEOS/O3 chemistry.
In the development of new chemical precursors, the different types of CVD systems must be considered. A variety of CVD systems are utilized in the semiconductor industry, and are typically divided into two groups: thermal systems and plasma enhanced systems. Thermal systems utilize thermal energy to disassociate the chemical precursors, where they react and deposit a layer or film on the substrate. Thermal CVD systems typically operate at atmospheric pressure (referred to as APCVD systems) or low pressure (referred to as LPCVD systems). In contrast, plasma enhanced systems utilize ionized gases (i.e., a plasma) to disassociate the chemicals. While the two types of systems are used to perform the same function, i.e. to deposit a layer on a substrate, the systems have very different reactor and system designs, and operate under very different reaction kinetics and process conditions. It has been found that while one process chemistry may work well for one type of CVD system, it is not well suited for the other type of CVD system. For example, silane and oxygen (SiH4/O2) as precursors are very reactive, and can be explosive, and due to this problem the TEOS/O3 precursor chemistry has found wide use in the thermal CVD type systems. The TEOS/O2 precursor chemistry has been found to be suitable when employed in plasma CVD type systems, however TEOS/O3 precursor chemistry has not. SiH4/O2 precursor chemistry has found use in plasma CVD systems.
While the above described precursor chemistry has found wide use in the semiconductor industry, there is a continuing need for the development of improved precursor chemistry and their processes, particularly as device densities decrease and the demands on the gap filling properties of the films increase. Moreover, the cost and/or consumption of certain conventional precursors is high, and it is desirable to develop new, less expensive and/or lower consumption precursors.
Accordingly, it is an object of the present invention to provide an improved precursor chemistry and method of depositing oxide films or layers on the surface of semiconductor substrates.
It is a related object of the present invention to provide a method of depositing a film which promotes reduced cost of ownership (CoO) of the CVD system.
In the present invention, a method of depositing oxide films or layers using volatile alkylsiloxane precursors is provided. Specifically, the alkylsiloxane precursors of the invention are of the formula: (CH3)3Si[OSi(CH3)2]nOSi(CH3)3 where n=1 and 2. Such precursors thermally react with ozone to produce silicon dioxide for depositing on the surface of semiconductor substrates, and of significant advantage are particularly useful for sub 0.18 micron device applications. In fact, a dimer of such alkylsiloxane, hexamethyldisiloxane, has been investigated earlier. Of particular advantage, the process is a thermal CVD method and does not require the complex addition of plasma CVD technologies. In addition, by co-injection of dopant precursors such as phosphorus and/or boron precursors with the alkylsiloxane precursor in the presence of ozone, phosphorusilicate glass (PSG), borosilicate glass (BSG) and borophosphorusilicate glass (BPSG) films can also be formed using the thermal CVD method of the present invention. The inventors have found that significantly lower chemical usage and excellent gap fill can be achieved by using the method of the present invention as compared to using conventional TEOS, where the same film quality and deposition rate were maintained. Further, according to one embodiment of the present invention, octamethyltrisiloxane (OMTS) was mixed with ozone in the gas phase. It was found that this OMTS process generated less particulates in the exhaust lines as compared with conventional TEOS processes, which can significantly reduce chamber exhaust cleaning during high volume manufacturing. The inventors have also found that the deposition rate of silicon dioxide according to the method of the present invention is much less sensitive to wafer temperature than conventional processes, which is a very significant factor towards improvement of the silicon dioxide deposition thickness uniformity.